BIOL 121 Lecture Notes - Lecture 28: Catecholamine, Gonadotropin, Luteinizing Hormone
Document Summary
Only tissue with the appropriate receptor will respond to a given hormone. Number of receptors for a specific hormone can be up- regulated or down- regulated. When effectiveness of one hormone is increased by a second hormone, the 2nd hormone is said to be permissive to the first. Up-regulation is one possible mechanism of permissiveness. Catecholamines and peptide hormones bind to plasma-membrane receptors, triggering: Activation of g proteins that are coupled to effector proteins (which are enzymes or ion channels) Changes in enzyme activity very rapidly effect cell function. Effects of polar hormones are short-lived (min-hours) due to rapid metabolism of hormone. Steroids and thyroid hormones bind to intracellular receptors, triggering: Change in transcription and protein synthesis rate. Circulate bound to plasma proteins (carriers), but only free fraction of hormone can diffuse into cell and carry out its action. Changes protein synthesis affect target cells slowly. Effects of non-polar hormones are long-lived (hours to days)
